The long term objective of this research is to improve the health of patients with End Stage Renal Disease who require hemodialysis. This proposed study is ancillary to the Frequent Hemodialysis Network (FHN) trial, a trial designed to determine if daily dialysis in a center, or nocturnal dialysis at home every night will substantially improve those factors that are responsible for the high mortality of dialysis patients. The proposed studies stem from two lines of reasoning. First, the FHN trial offers an unparalleled opportunity to determine if frequent dialysis will improve patients'cognitive function. The majority of the literature indicates that large numbers of dialysis patients have cognitive defects, but whether today's dialysis patients will improve their cognitive function with frequent dialysis is not so clear. We submit that the tests that will be used to measure cognitive function in the FHN trial as presently designed are not sensitive or specific enough to make clear conclusions. Second, the practical effects of improvements in cognitive function (as measured by modern tests) on real-life function is not clear. We propose to conduct a series of sensitive cognitive function tests on a subset of patients who will be enrolled in the FHN trial to determine if cognitive function is improved, and if so, which aspects are improved to the greatest extent. We will make these measurements on 260 patients located in 11 sites where patients will be randomized to conventional dialysis or to nocturnal dialysis, and another 5 sites where patients will be randomized to conventional dialysis or daily dialysis. In a second part of the study, we will begin an assessment of the relationship between cognitive impairment exhibited by dialysis patients and their ability to perform driving tasks in a driving simulator. With these measurements we will be able to determine which cognitive functions improve with frequent dialysis and which cognitive functions predict impaired driving skills in dialysis patients. The importance of these studies to the public health relates to improved health and function of patients who have kidney failure and who require dialysis. Knowing which impaired cognitive functions predict impaired driving skills will help develop strategies to improve cognition and thus enhance safe driving. Such strategies have the potential to make the highways safer for everyone.